Celtic deity vs immortal

Celtic deity and immortal both are nouns.

Word	Noun	Adjective	Verb	Adverb
Celtic deity	Yes	No	No	No
immortal	Yes	Yes	No	No

As nouns, immortal is a hypernym of Celtic deity; that is, immortal is a word with a broader meaning than Celtic deity:

Celtic deity: a deity worshipped by the Celts
immortal: any supernatural being worshipped as controlling some part of the world or some aspect of life or who is the personification of a force

Other hypernyms of Celtic deity include deity, divinity, god.

Celtic deity (noun)	immortal (noun)
a deity worshipped by the Celts	any supernatural being worshipped as controlling some part of the world or some aspect of life or who is the personification of a force
	a person (such as an author) of enduring fame

Celtic deity (adjective)	immortal (adjective)
	not subject to death